1. Field of the Invention
The present invention relates to a method of manufacturing a display device, and more particularly, to a manufacturing method that can be applied to a display device having a wall-shaped electrode that is formed so as to protrude from a substrate surface.
2. Description of the Related Art
In recent years, as a property of a liquid crystal display device is improved, there is a demand for the development of products that enable a WVGA display of 800×480 pixels even in a small and medium-sized liquid crystal display device of 3 to 4 inches. However, in the small and medium-sized liquid crystal display panel that enables the WVGA display, it is necessary to form a plurality of display pixels (hereinafter, referred to as simply ‘pixels’) in a limited display area, and thus a width of one pixel is about 30 μm. For this reason, there is a demand for further increase in aperture ratio and in display mode efficiency.
For example, JP6-214244A discloses a liquid crystal display device as a liquid crystal display device that increases the display mode efficiency. In the liquid crystal display device, paired electrodes are formed at two ends of a pixel area, an image signal is applied to one electrode (pixel electrode, source electrode) of the electrodes, and a common signal as a reference signal is applied to the other electrode (common electrode) so as to generate an electric field (so-called horizontal electric field) that is parallel to a principal surface of a liquid crystal display panel, and thus liquid crystal molecules are driven. In particular, in the liquid crystal display device, since the pixel electrode and the common electrode are formed so as to protrude toward a second substrate from a principal surface of a first substrate, the liquid crystal display device has a wall-like electrode shape that is formed such that an extension direction thereof is perpendicular to the principal surface of the first substrate. By configuring the liquid crystal display device in such a manner, the display mode efficiency can be improved by equalizing the density of lines of electric force in both an area close to the first substrate and an area far from the first substrate (area close to second substrate).
However, in the liquid crystal display device, an area is formed where an electrode is not present between wall electrodes disposed in a pixel boundary and a pair of common electrodes (hereinafter, referred to as pseudo wall electrodes) disposed between the wall electrodes. In other words, in the pixel boundary portion, two wall electrodes (for example, common electrodes) corresponding to each of adjacent pixels are disposed in parallel with each other, and thus other electrodes are not formed between the two wall electrodes formed in the pixel boundary.
In this regard, for example, there is a liquid crystal display device in which a wall-shaped common electrode formed along an extension direction of a pair of wall electrodes is formed in an area between wall electrodes disposed in a pixel boundary. In the liquid crystal display device, a flat plate-shaped electrode (transparent electrode) that extends from the wall electrodes is also formed in an area between the wall electrodes formed in the pixel boundary and the wall-shaped common electrode. Further, the electrode extending from the wall electrodes is formed together with the wall-shaped common electrode with an insulating film interposed therebetween along a side wall surface of the wall-shaped common electrode. In this configuration, in the wall-shaped common electrode, a conductive film is formed so as to cover ahead surface and a side wall surface of a columnar body that extends in a long-side direction of a pixel. In particular, a line of electric force leading to the conductive film that is formed in the head surface of the columnar body with a liquid crystal layer interposed therebetween is formed in the wall-shaped common electrode, and thus liquid crystal molecules are driven. For this reason, in this pixel structure, it is necessary to expose the conductive film formed in the head surface of the columnar body and to cover the conductive film formed in the side wall surface of the columnar body by the conductive film extending from the wall-shaped electrode.
On the other hand, thin films such as a thin film transistor and a pixel electrode that forms the liquid crystal display device are generally formed using a well-known photolithography technique. For example, in forming the wall-shaped common electrode that is formed so as to be exposed from the conductive film extending from the wall electrode, a conductive film to cover a cuboid and an insulating film to cover the conductive film are formed, and another conductive film is formed in an upper layer thereof. Next, after applying a resist material formed of a photocurable resin or the like thereto, a resist surface is irradiated with light having a desired pattern, and it is then developed, and thus a resist having a desired shape is formed. Thereafter, the conductive film that is exposed from the resist is etched using the resist as an etching mask (protective film) so that only the conductive film of the head surface of the cuboid is exposed from the conductive film that forms the wall-shaped electrode.
However, in forming the thin film using photolithography, When exposing the resist, the resist is exposed using a well-known photomask. At this time, the positioning accuracy between the photomask and the first substrate becomes very important. For example, when only the head surface of the columnar body is etched, that is, when a wall-shaped pixel electrode is formed, there is a need to form an etching mask to expose only the head surface of the cuboid. In this case, when a positive resist in which a light-irradiated portion is removed by a developing process is used, an exposing process is performed using a photomask in which only the head surface of the columnar body is irradiated with light. However, since it is necessary to form the conductive film in the side wall surface portion of the columnar body along the side wall surface, the positioning accuracy in a direction of the side wall surface of the columnar body is required to be higher than the thickness of the conductive film.
In particular, the side wall surface of the columnar body of which a cross-section has a rectangular shape, a transparent conductive film that is formed so as to cover the head surface, and the insulating film which is a lower layer thereof have significantly small thicknesses. For this reason, the positioning accuracy between the photomask and the first substrate needs to be significantly high, and it is necessary to use a photomask with a significantly high formation accuracy, and thus there is a demand for the development of a technique for forming a wall-shaped common electrode at the same level of accuracy as a thin film formed in an in-plane direction of the first substrate.